1. Field of the Invention
The present invention relates generally to electronic control systems, and particularly to an automotive electronic control system in which a first electronic control unit (ECU) is connected by a communication line to a second ECU, the first ECU being programmed to erase abnormality data generated at the second ECU when the first ECU is being reloaded.
2. Description of the Related Art
Presently, electronic control units, such as that disclosed in Japanese Unexamined Patent Publication No. Hei. 6-272611 control car engines and the like via a control program stored in nonvolatile memory whose content can be erased and rewritten. Therefore, programs stored therein can be reloaded even after the unit is supplied to the marketplace.
During normal operation, an electronic control unit having a program reloading capability as described above controls a control object, such as an engine, in accordance with a program held in reloadable nonvolatile memory. However, when the controller receives a reload command from an externally connected data reloading device, the controller executes reload processing to overwrite the stored content of the reloadable nonvolatile memory with a new program transmitted from the data reloading device.
In automotive vehicles of recent years, vehicle control systems have been utilized wherein each of a plurality of interconnected ECUs controls a designated control object, such as an engine or a transmission, while performing data communication with the other electronic control units to improve control performance and reduce vehicle wiring. In such a vehicle control system, each ECU uses the following kind of method to monitor the normality of the other ECUs and the communication line interconnecting the ECUs, and stores corresponding abnormality information when determining that there is an abnormality.
For example, each ECU may determine that another ECU with which it is communicating, or the communication line itself, is abnormal when, after transmitting a request message to the other ECU requesting predetermined data, the ECU does not receive a reply message from that ECU within a predetermined time. Upon determining that there is such an abnormality, it stores abnormality information in its own nonvolatile memory (for example, backup RAM or EEPROM backed up with a battery voltage).
However, when the ECU mentioned above is utilized in a vehicle control system, the following problems often occur.
For example, while the program of the ECU is being reloaded, the ECU cannot send a reply message in response to request a message from another ECU during reload processing. Consequently, an ECU which transmits a request message makes the erroneous determination that the reloading ECU is abnormal.
When abnormality information indicating that an ECU whose program has been reloaded is abnormal remains stored in the determining ECU, the determining ECU continues to perform its own control operations with control data set to default values. Consequently, there is a decrease in control performance.
Also, when the abnormality information stored in the ECUs is analyzed, the ECU erroneously determined to be abnormal often is unnecessarily replaced.
The following methods for erasing abnormality information stored in an ECU are set forth, for example, in the Toyota Cavalier Service Manual.
[1]: Connect a fault diagnosis unit to the ECU in which the erasure is required, and perform processing to erase the abnormality information in that ECU by supplying special commands from the fault diagnosis unit.
[2]: Among fuses mounted in the vehicle, remove the fuse corresponding to the ECU in which the erasure is required. By this means, because the power supply from the battery to the ECU in which the erasure is required is cut off, if the abnormality information is stored in backup RAM, that abnormality information can be erased.
[3]: Remove a battery cable of the vehicle from a battery terminal. By this means, because the supply of power from the battery to all of the ECUs is cut off, as in [2] above, if the abnormality information is stored in backup RAM then that abnormality information can be erased.
However, with the methods of [2] and [3] above, when the abnormality information is stored in reloadable nonvolatile memory such as an EEPROM or flash memory, the abnormality information cannot be erased. Even if the abnormality information is stored in backup RAM, because generally not only abnormality information but also learned values and the like used for control are stored in backup RAM, with the methods of [2] and [3] valuable learned values accumulated up to that time are also erased, and the control performance consequently decreases.
With the method of [1] above, on the other hand, work from connecting the fault diagnosis unit to each of the ECUs making up the control system in turn is necessary, and this requires a significant amount of labor.
Furthermore, with the methods of [1] through [3] above, because human labor is required to erase the abnormality data, the possibility that some abnormality information will not be erased is increased.